1. Field of the Invention
The present invention relates to nebulizers, and more particularly to devices and methods for detecting the level of a drug solution in a nebulizer.
2. Description of the Related Art
Various nebulizers include sensors that sense when the drug solution chamber is empty, thereby signaling that the drug has been completely delivered. For example, U.S. patent application Ser. No. 11/367,486 (now U.S. Publication No. 2006/0201501) and Ser. No. 11/367,075 (now U.S. Publication No. 2006/0243274), both of which were filed Mar. 3, 2006, disclose the use of a probe in a drug solution chamber. The probe detects an AC signal that passes from an acoustic wave generator through the liquid drug to the probe. When the drug level falls below the probe, the circuit is interrupted, thereby indicating that the drug level is below the level of the probe. One potential drawback to this system is that such drug level sensors are disposed within the drug solution chamber in direct contact with the drug solution. In addition, the effectiveness of such probe-based drug level sensors relies upon the ability of the drug solution to conduct the A/C signal to the probe.